Miniaturized potentiometer

ABSTRACT

A rotary-contact potentiometer which is primarily intended to be employed in miniaturized hybrid circuits. It comprises a metallic casing which contains the rotary slider and its actuating member and a circular resistive track deposited on an insulating support. The casing has an open structure and is provided on one of its faces with a circular opening for guiding and centering the slider-actuating member. The opposite face to said opening is the external face of the insulating support of the resistive track. Three metallized zones are formed on said face of the insulating support for fixing the potentiometer and establishing electrical connections between the potentiometer and the electric circuit.

United States Patent 1191 Falco 338/174 Maurice July 24, 1973 [54] MINIATURIZED POTENTIOMETER [75] Inventor: Jean Maurice, Nice, France jg' 'gfz gffiz fg g":9 [73] Assignee: Societe Francaise De Attorney-Irvin S. Thompson et al.

LElectro-Resistance, Nice, France [22] Filed: Aug. 8, 1972 [57] ABSTRACT [2]] Appl. No.: 278,865 A rotary-contact potentiometer which is primarily intended to be employed in miniaturized hybrid circuits. It comprises a metallic casing which contains the rotary [30] Foreign Apphcauon Priority Data slider and its actuating member and a circular resistive Aug. 31, France track deposited on an insulating pp The casing has an open structure and is provided on one of its [52] US. Cl. 338/162, 338/18; faces with a circular opening for guiding and centering [5 ..3..3..-..i.... the slider actuating member. The pp faca to Said [5 8] F 9 d o 3 l opening is the external face of the insulating support of I 1 the resistive track. Three metallized zones are formed on said face of the insulating support for fixing the po- [56] References Cmd tentiometer and establishing electrical connections be- UNITED STATES PATENTS tween the potentiometer and the electric circuit. 3,111,640 11 1963 D' 1 33s 184X 3,581,265 511971 la I 13 Claims, 16 Drawing Figures Patented July 24, 1973 4 Sheets-Sheet 1 Patented July 24, 1973 3,748,626

4 Sheets-Shoot 2 Patented July 24, 1973 4 Shouts-Shoot Patented July 24, 1973 I 3,748,626

4 Shoots-Shoot 4 MINIATURIZED POTENTIOMETER This invention relates to a rotary-contact potentiometer, especially of the miniature type which is primarily intended to be employed in hybrid and integrated circuits.

Potentiometers having small dimensions have already been disclosed in French patents filed by the present Applicant and published under No. 1,402,082 and No. 1,481,999.

These devices prove wholly satisfactory both from the point of view of fabrication and operation. However, the structural design of these potentiometers which governs the method of manufacture imposes dimensional requirements such that these devices cannot in practice be incorporated in the miniaturized hybird circuits which the electronic equipment industry is capable of producing at present time.

The object of the present invention is to produce a potentiometer of rugged construction which readily permits large-scale manufacture in spite of its very small dimensions, with the result that all operations which are necessary for integration of the potentiometer in hybrid circuits are thus made possible, especially when said integration entails the well-known remelting method followed by ultrasonic cleaning in an organic solvent.

A further object of the invention is to permit selection of the potentiometer components from conductive and insulating materials which are capable of withstanding the temperatures attained at the time of application of the remelt technique without any attendant danger and which must be insensitive to the action of the solvents usually employed at the time of ultrasonic cleaning. Yet another object of the invention is to permit cleaning of the internal portions of the potentiometer before or after mounting of this latter on the hybrid circuit. In fact, by reason of the small dimensions of a potentiometer of this type as well as the low electric currents circulating within said circuits, the slightest superficial alteration of the active portions of the potentiometer is liable to give rise to appreciable modification of the resistance between the terminals, thereby resulting in failure of the entire circuit.

In accordance with the invention, the rotary-contact potentiometer which is primarily intended to be employed in miniaturized hybrid electric circuits and comprises a metallic casing which contains the rotary slider and its actuating member and a circular resistive track deposited on an insulating support, is characterized in that the casing has an open structure and is provided on one of its faces with a circular opening for guiding and centering the slider-actuating member and that the face opposite to said opening is the external face of the insulating support of the resistive track, three metallized zones which are separate from each other being formed on said face of the insulating support for fixing the potentiometer in position and establishing electrical connections between the potentiometer and the electric circuit.

The openings formed in the casing make it possible both to facilitate the assembly of the different components of the potentiometer and make these latter accessible to the cleaning solvent.

In a preferred embodiment of the invention, at least a number of the following components casing, slider and slider-actuating member are constituted by sheetmetal elements which are cutout, bent and/or diestamped.

The casing is preferably provided with a plurality of lugs which are folded-back towards the interior of this latter parallel to the face in which the circular opening is formed and applied both against the external face of the insulating support of the resistive track and against the internal face thereof.

In an advantageous embodiment, at least one of the lugs of the casing is applied against the external face of the insulating support, is placed over one of the three metallized zones of the insulating support and constitutes one of the output terminals of the potentiometer, the two other metallized zones being connected to the extremities of the circular resistive track by means of two conductive members which constitute the two other output terminals of the potentiometer.

Bending of the casing as contemplated by the invention permits positioning of the resistive track support without having recourse to methods of assembly such as clipping, crimping or bonding. Moreover, the aforesaid positioning of the resistive track support within the casing does not entail any modification of the shape of this latter, with the result that materials having high mechanical strength can be employed in the fabrication of the casing which is thus endowed with a very high degree of ruggedness.

The positioning above the weldable metallized zones of the resistive track support, on the one hand of the folded-back lugs of the casing and on the other hand of the conductive members which constitute the electrical output terminals, makes it possible to weld the potentiometer onto the electric circuits by means of the remelting method. Remelting results at the same time in welding of the conductive members to the support and in welding of said support to the casing.

The conductive members can be of variable shapes and sizes adapted to the configuration of the circuit with which the potentiometer is intended to be integrated.

Further particular features of the invention will become apparent from the following description.

In the accompanying drawings which are given by way of example but not in any limiting sense and in which one preferred embodiment of the invention is illustrated FIG. 1 is a view in perspective showing one embodiment of the potentiometer FIGS. 2 and 3 are two views in perspective of the slider-actuating member, looking respectively on one face and on the other face after said member has been rotated through FIGS. 4 and 5 are two views in perspective showing the casing after this latter has been rotated through 180 FIG. 6 is a view in perspective of the slider FIG. 7 is a view in perspective of the resistive track support FIGS. 8 and 9 are two views in perspective of the two conductive members which constitute two output terminals of the potentiometer FIG. 10 is an alternative form of a member shown in FIG. 8

FIG. 11 is a bottom plan view of the potentiometer FIG. 12 is a view in elevation showing one of the lateral faces of the potentiometer FIG. 13 is a view in elevation showing another lateral face of the potentiometer FIG. 14 is a top plan view and a half-sectional view taken along line XlV-XIV of FIG. 12

FIG. 15 is a view in elevation of the lateral face opposite to that of FIG. 13

FIG. 16 is a view in perspective showing the protective cap.

In the particular embodiment of the invention which is contemplated in the figures listed above, the potentiometer in accordance with the invention comprises a metallic casing 1 having a number of open portions and provided at the center of one of its faces with a circular opening 2 for guiding and centering the actuating member 3 of the slider 4.

The face opposite to said circular opening 2 is the external face of the insulating support 5 of the resistive track 6. As shown in FIG. 1 1, said face has three metallized zones 7, 8, 9 which permit of welding and are preferably tinned for fixing the potentiometer and establishing the electrical connections between this latter and the electric circuit.

The casing is preferably formed by cutting-out and bending of a sheet-metal element. This latter is preferably obtained from alloys having good electrical conductivity and high mechanical strength such as nickel silver and beryllium bronze. It is an advantage in addition to coat the casing with a protective layer formed by electrodeposition of a noble metal such as gold.

The casing 1 is provided with a plurality of lugs 10, ll, 12, 13 which are bent-back towards the interior of said casing at an angle of 90 and parallel to the face in which the circular opening 2 is formed. The lugs l0, 12, 13 are applied against the external face of the insulating support 5 forming the base of the potentiometer and partially cover the weldable metallic zone 7. The lug 11 is applied against that face of the support 5 which carries the resistive track 6. Said track has an annular shape and the two extremities of this latter are connected to two metallized zones l4, which are preferably tinned.

The insulating material which constitutes the support 5 is advantageously a ceramic material having an alumina base and the track 6 is constituted by a deposit of gold alloyed with palladium and applied by silk-screen process.

The conductive members l6, 17 are provided in the form of strips bent-back into a U shape and are positioned by clamping so as to cover the weldable zones 8 and 9 located on the outer face of the insulating support 5 as well as the weldable zones 14 and 15 which are connected to the extremities of the resistive track 6. Said conductive members can be provided with extension lugs having variable dimensions according to the configuration of the hybrid circuit on which the potentiometer is to be fixed. An alternative design of these conductive members is given in FIG. 10. Said members are preferably formed of nickel silver which may be coated if necessary with a thin protective layer of gold.

The actuating member 3 of the slider 4 is formed by cutting-out and die-stamping a metallic sheet and provided with a circular peripheral projection 19 for guiding and centering which permits pivotal motion of said member within the circular opening 2 of the casing. The actuating member is further provided with lugs 20, 21 and 22 for providing a mechanical coupling between said member and the slider 4. Two of said lugs 20 and 21 are cut from a diametrical slot 23 of said actuating member and are bent-back towards the interior of the casing at an angle of A third coupling lug 22 is also cut from said actuating member, the center of the lug 22 being preferably located at right angles to the extremities of the slot 23.

Said actuating member is preferably made of beryllium bronze and the surface of said member is protected against any chemical change by means of an electrodeposited layer of a noble metal.

The slider 4 is formed by cutting-out and bending a sheet-metal element. The slider comprises a flat portion 24 having the shape of a circular segment and carrying a resilient tongue 25 which is bent-back towards the interior of the casing.

Said tongue 25 is made up of at least three contact fingers which are intended to bear resiliently on the resistive track 6 and to sweep the surface of this latter the contact surfaces thus formed between the fingers and the track are substantially aligned on a straight line which passes through the center of the circle formed by said track.

The slider 4 is also provided with a diametrical slot 26 which has the same size as the slot formed in its actuating member 3 and into which penetrate the two coupling lugs 20 and 21 while bearing on the extremities of said slot 26. In order to strengthen the mechanical coupling between the actuating member 3 and the slider 4, there is also formed in said slider a slot 27, the lug 22 of the actuating member 3 being intended to fit within said slot. After the lugs 20 and 21 have been bent-back towards the surface of the slider 4, this latter is thus counter-braced against its actuating member, the circle which is circumscribed about the portion 24 having the shape of a circular segment of said slider being concentric with the opening 2 of the casing 1. The diameter of said circumscribed circle is larger than the diameter of the circular opening 2, with the result that the periphery of the circular portion 24 of said slider is applied against the internal edges of the opening 2. The slider 4 is preferably cut from a metallic sheet having a mechanical strength and elastic limit which is compatible with a contact force between the fingers and the resistive track of at least 60 g. By way of example, it is possible to employ a beryllium bronze subjected to heat treatment after cutting-out and bending so as to endow this latter with a Vickers hardness number of the order of 380. The slider 4 which is thus obtained is covered with a protective coating of a noble metal which affords a sufficient degree of resistance to the friction caused at the time of rubbing of the fingers on the track.

In order that the rotation of the slider 4 should be limited angularly, the slider-actuating member 3 is preferably provided with a projecting lug 28 which is abuttingly applied against a boss 29 carried by the easing 1.

The assembly of the above-mentioned elements can be carried out in a particularly simple and rapid manner and practically does not call for the use of any tool.

Referring to FIGS. 2 to 10, it is in fact apparent that, in order to assemble the potentiometer, it is only necessary to position the actuating member 3 within the circular opening 2 of the casing l and then to introduce the slider 4 within the casing by applying this latter against its actuating member 3 after having allowed the two lugs 20 and 21 to pass into the diametrical slot 26 and the lug 22 to pass into the slot 27 of the slider 4. When these two components are in position, it is only necessary to turn back the lugs 20, 21 and 22 against the surface of the slider by any suitable means, then to insert the support 5 of the resistive track 6 fitted with the conductive members 16 and 17 or the like by sliding within the casing l in the same manner as a drawer.

The assembly constitutes a highly compact unit having a very small volume (approximately 0.03 cm in the case of the potentiometer hereinabove described).

The potentiometer can then be placed on the circuit in the actual location in which it is intended to perform its function, the potentiometer being finally fixed on the circuit by means of the well-known method of remelting.

This remelting operation fixes the potentiometer by welding between the circuit and the conductive members l6 and 17 or the like and the lugs 10, l2, l3 and at the same time effects the welding of the conductive members to the support 5 by means of weldable zones 8 and 9 as well as the welding of the support 5 to the casing at the level of the lugs l0, l2, 13 by means of the weldable zone 7.

The circuit element which is fitted with the potentiometer or potentiometers in accordance with the invention can be dipped in a cleaning solvent which may be subjected if necessary to the action of ultrasonic waves in order that all parts of the circuit and of the potentiometer may thus be freed from any dirt, impurity, dust and the like which is liable to affect the reliability of the assembly as thus constituted.

Adjustment of the potentiometer is carried out by introducinga tool such as a screwdriver into the slot 23 which. is formed in the actuating member 3 and by causing this latter to pivot until the desired currentvoltage characteristics are obtained.

The projecting lug 28 is preferably resilient and is thus capable of bending under the action of an excessive couple exerted on the actuating member 3. As a consequence, it is not possible to damage the travellimiting device which recovers its efficiency as soon as the lug 28 has passed over the stop 29.

Since the slider-actuating member 3 is at the same electric potential as the slider 4 and the casing l, the aforesaid adjustment entails the need for an insulated tool or screwdriver this can be dispensed with by incorporating with the actuating member an insulating knob which could be engaged, for example, in the slot 23.

The potentiometer which is thus secured to its circuit and adjusted is preferably covered with an elastic cap 30 (shown in FIG. 16) which is fabricated from an elastomer material in order to protect the potentiometer against dust particles, chemical changes and mechanical impacts.

As is readily understood, the invention is not limited to the example hereinabovc described and it is possible to contemplate alternative forms of execution of the invention. In particular, both the lug 22 of the slideractuating member and the corresponding slot 27 formed in the slider may be dispensed with.

What we claim is l. A rotary-contact potentiometer which is primarily intended to be employed in miniaturized hybrid electric circuits and comprises a metallic casing which contains the rotary slider and its actuating member and a circular resistive track deposited on an insulating support, wherein the casing has an open structure and is provided on one of its faces with a circular opening for guiding and centering the slider-actuating member and wherein the face opposite to said opening is the external face of the insulating support of the resistive track, three metallized zones which are separate from each other being formed on said face of the insulating support for fixing the potentiometer in position and establishing electrical connections between the potentiometer and the electric circuit.

2. A potentiometer according to claim 1, wherein at least a number of the following components casing, slider and slider-actuating member are constituted by sheet-metal elements which are cut-out, bent and/or die-stamped.

3. A potentiometer according to claim 2, wherein the casing is provided with a plurality of lugs which are folded-back towards the interior of said casing parallel to the face in which the circular opening is formed and applied both against the external face of the insulating support of the resistive track and against the internal face thereof.

4. A potentiometer according to claim 3, wherein at least one of the lugs of the casing is applied against the external face of the insulating support, covers one of the three metallized zones of said insulating support and constitutes one of the output terminals of the potentiometer.

5. A potentiometer according to claim 4, wherein the two other metallized zones are connected to the extremities of the circular resistive track by means of two conductive members which constitute the two other output terminals of the potentiometer.

6. A potentiometer according to claim 1, wherein the slider-actuating member is provided with a circular peripheral projection for guiding and centering which piv ots within the circular opening of the casing.

7. A potentiometer according to claim 6, wherein the slider-actuating member has two lugs providing a mechanical coupling with the slider, said lugs being cut from a diametrical slot of said slider and bent-back towards the interior of the casing.

8. A potentiometer according to claim 7, wherein the slider has a diametrical slot into which penetrate the coupling lugs of the actuating member.

9. A potentiometer according to claim 8, wherein the slider is constituted by a plate carrying a resilient tongue provided with contact fingers, said plate being counter-braced against its actuating member.

10. A potentiometer according to claim 6, wherein the slider-actuating member is provided with a projecting lug abuttingly applied against a boss carried by the casing in order that the rotation of the slider may be limited angularly.

11. A potentiometer according to claim 6, wherein the slider-actuating member has a diametrical slot so as to permit of its actuation by means of a tool such as a screwdriver.

12. A potentiometer according to claim 1, wherein said potentiometer is covered with a protective elastic cap.

13. Miniaturized hybrid electric circuits comprising at least one rotary-contact potentiometer according to claim 1.

i l t 

1. A rotary-contact potentiometer which is primarily intended to be employed in miniaturized hybrid electric circuits and comprises a metallic casing which contains the rotary slider and its actuating member and a circular resistive track deposited on an insulating support, wherein the casing has an open structure and is provided on one of its faces with a circular opening for guiding and centering the slider-actuating member and wherein the face opposite to said opening is the external face of the insulating support of the resistive track, three metallized zones which are separate from each other being formed on said face of the insulating support for fixing the potentiometer in position and establishing electrical connections between the potentiometer and the electric circuit.
 2. A potentiometer according to claim 1, wherein at least a number of the following components : casing, slider and slider-actuating member are constituted by sheet-metal elements which are cut-out, bent and/or die-stamped.
 3. A potentiometer according to claim 2, wherein the casing is provided with a plurality of lugs which are folded-back towards the interior of said casing parallel to the face in which the circular opening is formed and applied both against the external face of the insulating support of the resistive track and against the internal face thereof.
 4. A potentiometer according to claim 3, wherein at least one of the lugs of the casing is applied against the external face of the insulating support, covers one of the three metallized zones of said insulating support and constitutes one of the output terminals of the potentiometer.
 5. A potentiometer according to claim 4, wherein the two other metallized zones are connected to the extremities of the circular resistive track by means of two conductive members which constitute the two other output terminals of the potentiometer.
 6. A potentiometer according to claim 1, wherein the slider-actuating member is provided with a circular peripheral projection for guiding and centering which pivots within the circular opening of the casing.
 7. A potentiometer according to claim 6, wherein the slider-actuating member has two lugs providing a mechanical coupling with the slider, said lugs being cut from a diametrical slot of sAid slider and bent-back towards the interior of the casing.
 8. A potentiometer according to claim 7, wherein the slider has a diametrical slot into which penetrate the coupling lugs of the actuating member.
 9. A potentiometer according to claim 8, wherein the slider is constituted by a plate carrying a resilient tongue provided with contact fingers, said plate being counter-braced against its actuating member.
 10. A potentiometer according to claim 6, wherein the slider-actuating member is provided with a projecting lug abuttingly applied against a boss carried by the casing in order that the rotation of the slider may be limited angularly.
 11. A potentiometer according to claim 6, wherein the slider-actuating member has a diametrical slot so as to permit of its actuation by means of a tool such as a screwdriver.
 12. A potentiometer according to claim 1, wherein said potentiometer is covered with a protective elastic cap.
 13. Miniaturized hybrid electric circuits comprising at least one rotary-contact potentiometer according to claim
 1. 